Abstract
Abstract. The importance of wind-blown mineral dust for cloud droplet formation is studied by considering (i) the adsorption of water on the surface of insoluble particles, (ii) particle coating by soluble material (atmospheric aging) which augments cloud condensation nuclei (CCN) activity, and (iii) the effect of dust on inorganic aerosol concentrations through thermodynamic interactions with mineral cations. The ECHAM5/MESSy Atmospheric Chemistry (EMAC) model is used to simulate the composition of global atmospheric aerosol, while the ISORROPIA-II thermodynamic equilibrium model treats the interactions of K+-Ca2+-Mg2+-NH4+-Na+-SO42−-NO3−-Cl−-H2O aerosol with gas-phase inorganic constituents. Dust is considered a mixture of inert material with reactive minerals and its emissions are calculated online by taking into account the soil particle size distribution and chemical composition of different deserts worldwide. The impact of dust on droplet formation is treated through the unified dust activation parameterization that considers the inherent hydrophilicity from adsorption and acquired hygroscopicity from soluble salts during aging. Our simulations suggest that the presence of dust increases cloud droplet number concentration (CDNC) over major deserts (e.g., up to 20 % over the Sahara and the Taklimakan desert) and decreases CDNC over polluted areas (e.g., up to 10 % over southern Europe and 20 % over northeastern Asia). This leads to a global net decrease in CDNC by 11 %. The adsorption activation of insoluble aerosols and the mineral dust chemistry are shown to be equally important for the cloud droplet formation over the main deserts; for example, these effects increase CDNC by 20 % over the Sahara. Remote from deserts the application of adsorption theory is critically important since the increased water uptake by the large aged dust particles (i.e., due to the added hydrophilicity by the soluble coating) reduce the maximum supersaturation and thus cloud droplet formation from the relatively smaller anthropogenic particles (e.g., CDNC decreases by 10 % over southern Europe and 20 % over northeastern Asia by applying adsorption theory). The global average CDNC decreases by 10 % by considering adsorption activation, while changes are negligible when accounting for the mineral dust chemistry. Sensitivity simulations indicate that CDNC is also sensitive to the mineral dust mass and inherent hydrophilicity, and not to the chemical composition of the emitted dust.
Highlights
Atmospheric aerosols from anthropogenic and natural sources adversely affect human health and influence the Earth’s climate, both directly and indirectly (Haywood and Boucher, 2000; Lohmann and Feichter, 2005; Andreae and Rosenfeld, 2008; IPCC, 2013; Kushta et al, 2014; Lelieveld et al, 2015)
This study assesses the impact of mineral dust on global cloud droplet number concentrations by using an interactive aerosol–chemistry–cloud–climate model (EMAC)
The “unified dust activation framework” (UAF) has been implemented into the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model to account for the effects of dust particles through both the hydrophilicity from adsorption and the acquired hygroscopicity from pollution solutes on cloud condensation nuclei (CCN) activity calculations
Summary
Atmospheric aerosols from anthropogenic and natural sources adversely affect human health and influence the Earth’s climate, both directly and indirectly (Haywood and Boucher, 2000; Lohmann and Feichter, 2005; Andreae and Rosenfeld, 2008; IPCC, 2013; Kushta et al, 2014; Lelieveld et al, 2015). The present work aims at advancing previous studies of dust influences on cloud droplet formation by comprehensively considering (i) the adsorption of water on the surface of insoluble dust particles, (ii) the coating of soluble material on the surface of mineral particles which augments their CCN activity, and (iii) the effects of dust on the inorganic soluble fraction of dust through thermodynamic interactions of semi-volatile inorganic species and sulfate with mineral cations. The ECHAM5/MESSy Atmospheric Chemistry (EMAC) model (Jöckel et al, 2006) is used to simulate aerosol processes, while the “unified dust activation framework” (Karydis et al, 2011a; Kumar et al, 2011a) is applied to calculate the CCN spectra and droplet number concentration by explicitly accounting for the inherent hydrophilicity from adsorption and acquired hygroscopicity from soluble salts by dust particles from atmospheric aging. The sensitivity of the simulations to the emitted dust aerosol load, the mineral dust chemical composition and the inherent hydrophilicity of mineral dust is considered
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call